1. Field of the Disclosure
The disclosure herein relates generally to downhole acoustic well logging apparatus and methods.
2. Background Information
Acoustic logging tools are commonly used for logging wellbores to estimate one or more properties of the formation surrounding the tools for the purpose of producing hydrocarbons (oil and gas) therefrom. One type of acoustic tool provides images of the wellbore wall. One such tool includes a rotating transducer that transmits acoustic signals toward the wellbore wall and receives acoustic signals reflected from the wellbore wall. The received acoustic signals are converted into electrical signals, which signals are amplified, typically by a constant gain amplifier, and then processed to determine certain downhole parameters, such as the amplitude and time of arrival of the received signals. The fluid in the wellbore attenuates the transmitted acoustic signals and the reflected signals. This attenuation of the acoustic signals, in large part, depends upon the type of fluid in the wellbore. The fluid in the wellbore may be a water-based mud or an oil-based mud. The fluid density varies among muds. The attenuation of the acoustic signals depends upon the type and density of the mud. The constant gains used to amplify the received acoustic signals in the acoustic logging tools sometimes produce noisy signals because of the continued ringing effect of the transmitted signals.
The disclosure herein provides an acoustic logging tool that mitigates some of the effects of transmitter ringing and other unwanted downhole acoustic signals on the signals received in response to the transmitted signals.